A unique virus complex causes Ageratum yellow vein disease

Abstract

Ageratum conyzoides L., a weed species widely distributed throughout southeast Asia, frequently exhibits striking yellow vein symptoms associated with infection by Ageratum yellow vein virus (AYVV), a member of the Geminiviridae (genus Begomovirus). Most begomoviruses have bipartite genomes (DNAs A and B), but only a DNA A has been identified for AYVV. We demonstrate that yellow vein disease of A. conyzoides results from co-infection by AYVV DNA A (2,741 nt) and a circular DNA that is approximately half its size (1,347 nt) that we designate DNA beta. Apart from the sequence TAATATTAC, common to all geminiviruses and containing the initiation site of rolling circle replication, DNA beta shows negligible sequence homology either to AYVV DNA A or to DNA B associated with bipartite begomoviruses. DNA beta depends on DNA A for replication and is encapsidated by DNA A-encoded coat protein and so has characteristics of a DNA satellite. However, systemic infection of A. conyzoides by DNA A alone is sporadic and asymptomatic, and DNA A accumulation is reduced to 5% or less of its accumulation in the presence of DNA beta. Therefore, DNA A and DNA beta together form a previously unrecognized disease-inducing complex. Our data also demonstrate that the nanovirus-like DNA 1 component associated with infected A. conyzoides plays no essential role in the disease and represents a satellite-like DNA. Furthermore, the satellite DNA previously found associated with tomato leaf curl virus is probably a defective DNA beta homologue.

Replication promiscuity of DNA-β satellites associated with monopartite begomoviruses; deletion mutagenesis of the Ageratum yellow vein virus DNA-β satellite localizes sequences involved in replication

“…The construction of infectious clones of AYVV and its associated satellite from A. conyzoides (pHNBin419 and pBinAYVVb) has been described by Tan et al (1995) and Saunders et al (2000). The BamHI insert of EpYVV clone pGEM-EYVVAM1 isolated from Eupatorium makinoi (Saunders et al, 2003) was cloned into BamHI/BglII-digested pIC19H (Marsh et al, 1984), and the insert was subsequently cloned into this BamHI-digested intermediate to produce pIC-EYVV2AM.…”

“…A DNA fragment was PCR-amplified from pBS-AYVVb/5, a full-length clone of AYVV DNA-b (Saunders et al, 2000), using primer V4711 (Supplementary Table S1) to mutate T 794 AG and C 795 AT and introduce an SpeI site at position 790. The SpeI 790 -SpeI 429 fragment was cloned into pBluescript (Stratagene) to produce pBS-bD1.…”

“…The appropriate SpeI inserts were then cloned into these SpeI-digested intermediates to produce pBS-bD1dimer and pBSbD2dimer. Using pBS-AYVV2b (Saunders et al, 2000) as a template, primers V4713 and V4723 (Supplementary Table S1) were used to mutate A 804 AT, A 805 AC, A 806 AT, A 1048 AG and A 1051 AC to introduce BglII sites at positions 801 and 1047. The BglII 1047 -1347/1-BglII 801 fragment was cloned into pGEM-T Easy to produce pGEMbD3.…”

“…Many of these apparently monopartite begomoviruses are associated with a small satellite, designated DNA-b, which is essential for maintenance of the disease. Since the description of a DNA satellite, referred to as sat-DNA, associated with the monopartite begomovirus tomato leaf curl virus (ToLCV) (Dry et al, 1997) and the isolation of the first DNA-b satellite from Ageratum conyzoides plants infected with Ageratum yellow vein virus (AYVV) (Saunders et al, 2000), more than 200 satellite sequences have been established from a range of weeds, vegetable and fibre crops in Africa and Asia, reflecting their diversity and impact on agriculture throughout the Old World (Briddon & Stanley, 2006). …”

Agroinfection of tobacco by croton yellow vein mosaic virus and designing of a replicon vector for expression of foreign gene in plant

“…There are two types of betasatellite associated monopartite begomoviruses depending upon whether or not the cognate betasatellite molecules are essential for inducing symptoms [8]. In the majority of these begomoviruses, betasatellite molecules are necessary for symptom development [3,8,14,29]. In the second group, betasatellite is dispensable [17,30].…”